As a drill used for, for example, drilling in machining processes, there is known a drill having a chisel edge formed in a tip of the drill. Since the chisel edge has a wedge shape with a very small rake angle and a small chip pocket, a very large thrust load is generated, compared to a cutting edge. In a drill having a chisel edge, since components of force in directions orthogonal to a thrust are generated, biting capability and centering capability are reduced. Therefore, a technique to improve chip discharging capability from a center part, or so-called thinning, is conducted by shortening the chisel edge to add a rake angle. However, when the chisel edge is shortened by thinning, there is a problem that rigidity of an edge is reduced. Also, since the chisel edge still remains, vibration and whirling of the drill is not avoidable, and there is a limit in hole accuracy.
Therefore, Patent Document 1 disclosed a technique to prevent components of force in directions orthogonal to a thrust of a drill from being generated by providing a conical projecting part integrally with a body at a chisel position of the drill. However, in the drill, a cutting edge is not formed in the conical projecting part. Thus, centering capability is obtained, but an enormous thrust load is generated, which is likely to cause buckling. In addition, since a distance from a tip end of the drill, namely, an apex of the conical projecting part, to a shoulder (i.e., a tip length) is extended, a region where process is unstably done, that is, a distance until the whole tip of the drill enters a work piece, is increased, thereby deteriorating hole accuracy. Moreover, since the conical projecting part is added to the tip of the drill, it is not possible to manufacture the drill by existing drill grinding or the like, thereby causing an increase in manufacturing costs.